facebook request reading and user_id geting issue

Hi im sending my request like this

 <?php 
          $app_id = "127736900693315";
 
          $canvas_page = "http://apps.facebook.com/greetingz";
 
          $message = "Dynamic_msg";
          $data_s="Dynamic_data";
 
 
          $requests_url = "https://www.facebook.com/dialog/apprequests?app_id=" 
                 . $app_id . "&redirect_uri=" . urlencode($canvas_page)
                 . "&message=" . $message."&data=".$data_s;
 
          if (empty($_REQUEST["request_ids"])) {
             echo("<script> top.location.href='" . $requests_url . "'</script>");
 
 
          } else {
 
          }
 ?>
 

this request is going ok but when receiver click on notification im fetching through request_ids code is below

    if(!empty($_REQUEST['request_ids'])) {
 
     $config = array(
         'appId' => '343704039016593',
         'secret' => '56e711bf93d4e46426aa662c8be8d5ef',
         'cookie' => true,
 
     );
        $facebook = new Facebook($config);
         echo  $user_id= $facebook->getUser(); //** 0 printing**
         $app_token = $facebook->getAccessToken();
 
             $requests = explode(',',$_REQUEST['request_ids']);
             foreach($requests as $request_id) {
 
         $request_content = json_decode(file_get_contents("https://graph.facebook.com/'".$request_id."_".$user_id."'?access_token=$app_token"), TRUE);
 print_r($request_content);  //**nothing is printing**
 
 
 $deleted = file_get_contents("https://graph.facebook.com/$request_id?access_token=$app_token&method=delete");       
 
 
 
 
 
             }
 

I dono whats wrong on my coding im trying almost 7 days and I checked tutorial online most of those are old now the API have updated. I cant get the user_id even ... do I need to send my request OAuth Dialog??
}

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